Tony Stark's flawed choices make him an extremely relatable character, but some of his mistakes range from questionable to absolutely terrible. Whether it's locking up superheroes in a secret prison or trying to make his armor faster with, uhhh, roller skates, Tony made some bone-headed decisions in the past. However, attempting to clone Thor has to be his biggest mistake ever.
The events of Civil War shook the superhero community with a group of young heroes called the New Warriors causing a tragedy in Stanford, Connecticut during a pitched battle with the explosive villain Nitro. As a result, the Superhero Registration Act was passed, requiring all heroes to reveal their identities to the government. Tony Stark took a hard line in support of the act, but he was opposed to by one of his oldest friends - Captain America. Though Tony had a number of heroes on his side, he decided he needed an edge to take on the likes of Cap. Unfortunately, during this time, Thor had passed from the mortal coil. So Tony decided to do the next best thing... and clone him.
Apparently Tony had some of Thor's hairs on file from their first encounter (because of course, he did). With the help of Reed Richards and Hank Pym, Tony used the DNA to clone Thor and then added Stark technology to further augment the genetically-engineered Norse god with cybernetics. Code-named Ragnarok, this new Thor was deployed by Stark in his battle with Captain America and made short work of the enemy offensive. However, it's extremely clear there is something wrong with the unhinged clone from the start. When the battle escalates, Ragnarok kills the superhero Goliath in cold blood while the assembled heroes helplessly watch on. Ultimately, Storm and Hercules are able to destroy Ragnarok with the clone's high-tech hammer.
The death of Goliath destroys any remaining trust Tony Stark had with Captain America and his allies. Worse, Thor would shortly return from the dead and make his displeasure with Iron Man known. If all of this wasn't bad enough, Ragnarok himself eventually returned from the dead, as it was revealed one of his co-creators - Hank Pym - was a Skrull imposter, setting into motions events which would lead to his return. Ragnarok would ultimately join the Dark Avengers.
Thor's cloning is Tony Stark at his most stubborn and egotistical. Civil War's treatment of Tony Stark shows why the comic remains divisive among fans. While the movie adaptation had Stark struggling with the events of Avengers: Age of Ultron as well as revelations about his parents' death, the Tony Stark of the comic is driven almost solely by the belief that he is right. His sanctimonious attitude leads him to spearhead the Registration Act any cost, leading to the death of Goliath at the hands of Ragnarok. Perhaps worse of all, Civil War ends with Tony Stark effectively learning nothing as he assumes command of SHIELD and enthusiastically looks to the future, ignoring all the blood spilled. While future storylines would redeem Tony Stark in the eyes of both readers and his colleagues, his cloning of Thor is emblematic of the Armored Avenger at his absolute worst.